Control system for automatic transmission

ABSTRACT

A control system for an automatic transmission for an automotive vehicle having at least a torque converter, a planetary gear unit, brake bands and clutches actuated by hydraulic servos, a manual valve, shift valves, line pressure control means, detectors for a plurality of parameters indicative of the operating conditions of the engine, and discriminating circuits for carrying out an automatic shift from one speed ratio to another. In the system, an electrically operated shift shock control valve is provided to make an on-off operation in response to a timing control signal applied from a timing controller so as to alleviate the shift shock occurring during a shift from one gear position to another.

United States Patent [111 3,750,495 Ito et al. 1 Aug. 7, 1973 1 CONTROLSYSTEM FOR AUTOMATIC 3,572,168 3/1911 Shirai at al 74mm.

TRANSMISSION [75] Inventors: Shin lto; Seitoku Kubo; Mashanao Hashimoto;Chihlro l-layashl, all of Toyota, Japan [73] Assignee: Toyota JidoshaKogyo Kabushlki Kalsha, Toyota-shi, Japan [22] Filed: June 10, 1971 [2]]Appl. No.: 151,851

[30] Foreign Application Priority Data Aug. 6, I970 Japan 45/68858 [52]US. Cl. 74/866 [51] Int. Cl B60k 21/00 [58] Field of Search 74/866 [56]References Cited UNITED STATES PATENTS 3,665,779 5/1972 Mori 74/866Primary Examiner-Lconard H. (ierin Attorney-Cushman, Darby & Cushman[57] ABSTRACT A control system for an automatic transmission for anautomotive vehicle having at least a torque converter, a planetary gearunit, brake bands and clutches actuated .by hydraulic servos, a manualvalve, shift valves, line pressure control means, detectors for aplurality of parameters indicative of the operating conditions of theengine, and discriminating circuits for carrying out an automatic shiftfrom one speed ratio to another. In the system, an electrically operatedshift shock control valve is provided to make an on-ofi' operation inresponse to a timing control signal applied from a timing controller soas to alleviate the shift shock occurring during a shift from one gearposition to another.

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saw auur 11 CONTROL SYSTEM FOR AUTOMATIC TRANSMISSION BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to fluidcontrolled automatic transmissions for automotive vehicles and moreparticularly to a control system comprising a combination of electricaland hydraulic means for use in such an automatic transmission.

2. Description of the Prior Art Fluid controlled automatic transmissionsfor automotive vehicles are generally provided with a planetary gearunit and a plurality of hydraulic servo actuated frictional engagingmeans so as to obtain a suitable speed ratio by suitably engaging anddisengaging these frictional engaging means. A change from one speedratio to another is called a shift, and a so-called shift shock occursduring a shift due to a variation in the torque and the number ofrevolutions of the rotary members including the engine. In order toalleviate this shift shock and eliminate a slow or rough speedchangingmotion thereby to provide a comfortable feeling in driving, it isdesirable to engage and disengage the frictional engaging means withproper timing and at a suitable rate depending on the running conditionsthe vehicle.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a control system foran automatic transmission for an automotivevehicle which comprises a unique combination of hydraulic and electricalcontrol means for alleviating the undesirable shift shock and providinga comfortable feeling in driving due to the elimination of a slow andrough speed-changing motion.

Another object of the present invention is to provide a control systemof the above character which comprises an electrically operated controlvalve for controlling fluid pressure supplied to the hydraulic servosand a timing controller for applying a suitable timing control signal tothe electrically operated control valve to control the operation of thisvalve, depending on the running conditions of the vehicle therebydelicately controlling the rate of engagement and disengagement as wellas the timing of engagement and disengagement of the frictional engagingmeans.

In accordance with one aspect of the present invention, there isprovided, in an automatic transmission for an automotive vehicle, fortransmitting torque between a driving shaft and a driven shaft, acontrol system comprising frictional engaging means provided with fluidpressure operated servo means and arranged for the transmission oftorque between said driving and driven shafts, a source of fluidpressure for supplying fluid under pressure, for actuating saidfrictional engaging means, fluid passage means leading from said fluidpressure source to said frictional engaging means, fluid passagechange-over valve means disposed in said fluid passage means forselectively distributing fluid under pressure to said frictionalengaging means, signal generator means including at least a signalgenerator for generating an electrical signal responsive to the runningconditions of the vehicle thereby controlling said fluid passagechange-over valve means, fluid pressure control means for controllingthe pressure of fluid supplied to said frictional engaging means throughsaid fluid passage change-over valve means, and timing control means forgenerating an electrical signal for controlling the operation timing ofsaid fluid pressure control means in response to the output signaldelivered from said signal generator means, whereby said fluid pressurecontrol means is subject to on-off control during a shift from one gearposition to another which is followed by a variation in the torque beingtransmitted between said driving and driven shafts so as to control thefluid pressure supplied to said frictional engaging means therebyensuring smooth transmission of the torque between said driving anddriven shafts during the shift.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic sectional view ofan automatic transmission to which the present invention is applied.

FIG. 2 is an enlarged sectional view taken on the line IIII in FIG. 1with parts cut away to show in detail the relation between an idler gearnot shown in FIG. 1 and the sun gear and planet pinion.

FIG. 3 is a diagrammatic view showing the structure of a hydrauliccontrol section of a control system according to the present invention.

FIG.'4 is a chart showing the manner of increase relative to time of thefluid pressure supplied to hydraulic servos during a shift when thefluid pressure is controlled by a solenoid operated control valve.

FIG. 5 is a diagrammatic view showing a partial modification of thearrangement shown in FIG. 3, in which two solenoid operated controlvalves are used to control the rate of. increase in the fluid pressuresupplied to the hydraulic servos.

FIG. 6a is a diagrammatic view showing another partial modification ofthe arrangement shown in FIG. 3, in which a fluid pressure regulatingvalve is combined with the solenoid operated control valve forcontrolling the rate of increase in the fluid pressure supplied to oneof the hydraulic servos.

FIG. 6b is a diagrammatic view showing a further partial modification ofthe arrangement shown in FIG. 3, in which an orifice control valve iscombined with the solenoid operated control valve for controlling therate of increase in the fluid pressure supplied to one of the hydraulicservos.

FIGS. 7a and 7b are a block diagram showing the structure of anelectrical control section of the control system according to' thepresent invention.

FIG. 8 is a circuit diagram showing the structure of a throttle positiondetector preferably used in the electrical control section.

FIGS. 9a and 9b are a side elevation view and a front elevation viewrespectively of an output shaft r.p.m. detector preferably used in theelectrical control section.

FIG. 10 is a block diagram showing the structure of a DA converterpreferably used in the electrical control section and connected with theoutput shaft r.p.m. detector for delivering a signal representative ofthe r.p.m. of the output shaft.

FIG. 11 is a circuit diagram showing the structure of a discriminatingcircuit and an associated feedback circuit preferably used in theelectrical control section for generating a shift control signal.

FIG. 12 is a chart showing the relation between the output shaft r.p.m.signal and the throttle position signal depending on which, the outputfrom the discriminating circuit is determined.

FIG. 13 is a circuit diagram showing the structure of anotherdiscriminating circuit which compares a signal representative of therpm. of the engine with a reference voltage and delivers its outputdepending on the relation therebetween.

FIG. 14 is a circuit diagram showing the structure of a timing controlcircuit preferably used in the electrical control section.

FIG. 15 is a graphic illustration of input and output waveformsappearing at various parts of the timing control circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An automatic transmissioncontrolled by a control system embodying the present invention isschematically shown in FIGS. 1 and 2. The control system comprises ahydraulic control section as shown in FIG. 3 and an electrical controlsection as shown in FIGS. 7a and 7b.

Referring to FIGS. 1 and 2, the transmission comprises a hydraulictorque converter unit and a planetary gear unit arranged to providethree forward speeds and one reverse speed. The torque converter unit isof known construction including a pump impeller 2, a turbine impeller 3and a stator 4. The pump impeller 2 is directly connected to thecrankshaft 1 of an engine, and the turbine impeller 3 is connected to aturbine shaft 5 so that a rotational force can be transmitted to theplanetary gear unit disposed at the output side of the torque converterunit. The planetary gear unit includes two multiple disc clutch meansand two brake band means released and engaged by associated hydraulicservo means, a spray type one-way clutch, and a planetary gear traincomposed of sun gears and planet pinions. The turbine shaft 5 isconnected by means of a front clutch 6 to an intermediate shaft 8carrying an input sun gear 9 thereon and is further connected to areverse sun gear 10 by means of a rear clutch 7. A brake band means 22(hereinafter to be referred to as a front brake band) encircles the rearclutch 7 for controlling the reverse sun gear 10 and is actuated by ahydraulic servo. The input sun gear 9 meshes with each gear 12 of aplurality of, for example, two or three planet pinions 11. The reversesun gear 10 meshes with idler gears (shown in FIG. 2) which are eachrotatably mounted by a pin 14 fixed at one end to a carrier 13, and theidler gears 15 in turn mesh with gears 16 of the planet pinions 11. Therearmost gear 17 of each planet pinion l1 meshes with a gear 19 mountedat the front end of an output shaft 18 of the transmission. The planetpinions 11 having the gears 16, 12 and 17 and the idler gears 15 arecarried by the carrier 13 by means of pinion pins 20 and 14respectively. A brake band means 21 (hereinafter to be referred to as arear brake band) encircles the carrier 13 for applying the brake to thelatter and is actuated by a hydraulic servo. A spray type one-way clutch23 is associated with the carrier 13 for restricting the rotation of thecarrier 13 in one direction.

With the above structure, three forward speeds and one reverse speed canbe obtained by selectively actuating the elements above described.

First speed The front clutch 6 and the rear brake band 21 are actuated.(However, when the transmission is driven from the engine, the rearbrake band 21 may not be actuated since the one-way clutch 23 is alsoactuated to give the same result as that obtained with the actuation ofthe rear brake band 21. In this case, however, no driving force istransmitted from the output shaft 18.) With the front clutch 6 and therear brake band 21 so actuated, the rotation of the turbine shaft 5 isdirectly transmitted to the input sun gear 9 through the front clutch 6.Due to the fact that the carrier 13 is locked against rotation by therear brake band 21, the pinion pins 20 are also held stationary and therotation of the turbine shaft 5 is transmitted from the gear 9 to thegears 12, thence through the gears 17 to the gear 19 on the output shaft18 in a speed reduction relation thereby providing the first speed.

Second speed The front clutch 6 is kept actuated and the front brakeband 22 is actuated while releasing the rear brake band 21. Thus, theinput sun gear 9 is rotated in unison with the turbine shaft 5, but therear clutch drum, hence the reverse sun gear 10 is locked againstrotation by the front brake band 22. In this state, the rotation of theturbine shaft 5 is directly transmitted to the input sun gear 9 torotate the latter and the reaction of the reverse sun gear 10 causesrotation of the carrier 13 in the same direction as the direction ofrotation of the input sun gear 9 so that the gear 19, hence the outputshaft 18, carrying the gear 19, is rotated at a reduced or second speed.

Third speed The third speed can be obtained by engaging both the frontand rear clutches 6 and 7. The input sun gear 9 and the reverse sun gear10 are rotated in unison and the whole planetary gear system isunitarily rotated so that the turbine shaft 5 and the output shaft 18are rotated in a 1 1 relationship.

Reverse When reversing, the rear clutch 7 and the rear brake band 21 areactuated. The carrier 13, hence the pinion pins 14 and 20 are therebylocked against revolution, and the rotation of the turbine shaft 5 istransmitted through the rear clutch 7 to the reverse sun gear 10, thencethrough the idler gears 15 and the gears 16 and 17 of the planet pinions11 to the gear 19 mounted on the output shaft 18 so that the outputshaft 18 is rotated in the reverse direction.

Referring to FIG. 3, the hydraulic control section of the control systemincludes a hydraulic actuating circuit to which fluid under pressure issupplied by a pump 101 which may be a gear pump, vane pump or any othersuitable pump. The pump 101 is driven by a shaft directly connected tothe engine and draws thefluid from a fluid reservoir 102 through a fluidstrainer 102' to discharge the fluid under pressure into a fluid passage121. The fluid passage 121 leads to a pressure regulator valve 105 and amanual valve 120. The pressure regulator valve 105 is of a typeconventionally employed in automatic transmissions for automotivevehicles and includes a spring 106 and a valve spool 105' disposed inthe valve body. The valve spool 105 is provided with a plurality ofdifferent lands so as to carry out the pressure regulation by utilizingthe balance between the force of the spring 106 and the fluid pressuresapplied to spaced valve chambers 108 and 109. The fluid pressureregulated by this pressure regulator valve 105 is called a linepressure. The fluid pressure applied to the valve chamber 108 iscontrolled by means of the manual valve 120 and a relay valve 150, whilethe fluid pressure applied to the valve chamber 109 is controlled by aline pressure control solenoid 115. The on-off control of the linepressure control solenoid is accomplished by a signal applied from theelectrical control section of the system depending on the drivingconditions of the vehicle.

The manual valve 120 is connected with a shift lever (not shown)disposed adjacent to the drivers seat and takes one of the P, R, N, D, 2and L positions. When the manual valve 120 takes anyone of the D, 2 andL positions, fluid under pressure is supplied to a fluid passage 124 andcooperates with a spring 150 engaging a valve element of the relay valve150 to urge the valve element to its lower position so that the linepressure in the fluid passage 121 is applied to the upper valve chamber108 of the pressure regulator valve 105. When the line pressure controlsolenoid 115 is energized in this state, a solenoid orifice 115b isclosed by a plunger 116 and the line pressure is applied to the lowervalve chamber 109 of the pressure regulator valve 105. Thus, the linepressure regulated by the pressure regulator'valve 105 is represented bya constant lo'w fluid pressure P which is determined by the force of thespring 106 and the fluid pressures applied to the valve chambers 108 and109. On the other hand, when the line pressure control solenoid 1 is inthe deenergized state, the solenoid orifice l15b is kept open and thefluid pressure in the lower valve chamber 109 of the pressure regulatorvalve 105 is discharged to a pressure discharge port 115a so that theline pressure regulated by the pressure regulator valve 105 isrepresented by a constant high fluid pressure P which is determined bythe force of the spring 106 and the fluid pressure applied to the uppervalve chamber 108 of the pressure regulator valve 105. In the P, R or Nposition of the manual valve 120, the fluid passage 124 is exhausted andthe fluid pressure applied to the upper valve chamber 108 of thepressure regulator valve 105 is reduced by an amount which correspondsto the force of the spring 150' engaging the valve element of the relayvalve 150. When, in this case, the line pressure control solenoid 115 isin the on state, the linev pressure is applied to the lower valvechamber 109, while the fluid pressure which is reduced by the amountcorresponding to the force of the spring 150' is applied to the uppervalve chamber 108 of the pressure regulator valve 105. Thus, the linepressure regulated by the pressure regulator valve 105 is represented bya fluid pressure P which is higher than P On the other hand, when theline pressure control solenoid 115 is in its off state, the lower valvechamber 109 of the pressure regulator valve 105 is exhausted so that theline pressure regulated by the pressure regulator valve 105 isrepresented by a fluid pressure P which is higher than P The on-offcontrol of the line pressure control solenoid 115 will be described inthe later description relating to the electrical control section of thecontrol system.

The fluid pressure regulated by the pressure regulator valve 105 issupplied to the manual valve 120. When the manual valve 120 takes the Nposition, the fluid passage 121 is closed and valve chambers 122 and 123are exhausted. In the D position of the manual valve 120, the fluidpassage 121 communicates with fluid passages 124, 125 and 126 as seen inFIG. 3. The fluid passage 124 leads directly to a front clutch servochamber 6a, and the fluid passage 125 leads to the apply side 22a of aservo for the front brake band 22 through a l2 shift means 130, whilethe fluid passage 126 leads to a rear clutch servo chamber 7a and to therelease side 22b of the servo for the front brake band 22 through a 2-3shift means 135. When the manual valve is urged to the 2 position, thefluid passage 126 leading to the 2-3shift means 135 is exhausted and thefluid passages 124 and 125 communicate with the fluid passage 121. Whenthe manual valve 120 is urged to the L position, the fluid passages 125and 126 are exhausted and the fluid passages 124 and 127 communicatewith the fluid passage 121. The fluid passage 127 leads to the applyside 22a of the servo for the front brake band 22 through the l2 shiftmeans and a fluid passage 134 and leads further to the apply side 21a ofa servo for the rear brake band 21 through the l2 shift means 130 and afluid passage 127. When the manual valve 120 is moved to the R position,the fluid passages 124, 125 and 126 are exhausted and the fluid passages127 and 128 communicate with the fluid passage121. The fluid passage 128leads to the rear clutch servo chamber 7a through the 2-3 shift means135.

The l2 shift means 130 comprises a l2 shift valve element 131, a l2shift solenoid 132, and a spring 131' engaging the valve element 131.The l2 shift solenoid- 132 includes a plunger 133, a spring 133' and acoil 132'. Fluid under pressure is supplied from the fluid passage 121through an orifice 1214 to a chamber 121 disposed between the right-handend of the l2 shift valve element 131 and the l2 shift solenoid 132. Thel2 shift solenoid 132 is controlled by a signal applied from theelectrical control section of the system. When no current is supplied tothe l2 shift solenoid 132, the plunger 133 is kept in its leftward(extended) position by the force of the spring 133' thereby closing asolenoid orifice 132b so that the l2 shift valve element 131 is urged toits leftward (retracted) position by fluid pressure in the chamber 121.When current is supplied to the l2 shift solenoid 132, the plunger 133is urged to its rightward (retracted) position by the electromagneticforce and fluid under pressure in the chamber 121' is discharged to apressure discharge port 132a through the solenoid orifice 1321;. Thediameter of the orifice 121a is selected to be significantly smallerthan that of the orifice 1321; so that any substantial residual pressuremay not exist in the chamber 121' when the l2 shift solenoid 132 isenergized. Thus, the l2 shift valve element 131 is urged to itsrightward (extended) position by the force of the spring 131'.

The 2-3 shift means 135 comprises a 2-3 shift valve element 136, aspring 136 engaging the valve element 136, and a 2-3 shift solenoid 137.The structure of the 2-3 shift solenoid 137 is the same as that of thel2 shift solenoid 132. Fluid under pressure is supplied from the fluidpassage 124 through an orifice 124a to a chamber 124 disposed betweenthe right-hand end of the 2-3 shift valve element 136 and the 2-3 shiftsolenoid 137. The diameter of the orifice 124a is selected to be smallerthan that of solenoid orifice 13712. When current is supplied to the 2-3shift solenoid 137, fluid under pressure in the chamber 124' isdischarged to a pressure discharge port 1370 through the orifice 137b sothat the 2-3 shift valve element 136 is urgedto its rightward (extended)position by the force of the spring 136'. When no current is supplied tothe 2- 3 shift solenoid 137, the solenoid orifice 137b is kept closed bythe solenoid plunger 138 and the 2-3 shift valve element 136 is urged toits leftward (retracted) position by fluid pressure in the chamber 124'.

TABLE 1 2-3 solenoid Front Rear Front Rear brake brake clutch clutchband band Position of manual valve It will be seen from Table 1 that thel-2 shift solenoid 132 is on or energized in the D position-1st speed, 2position-lst speed and L position-2nd speed and is off or de-energizedin the D position-2nd speed, D position- 3rd speed, 2 position-2ndspeed, L position-1st speed and R position, while the 2-3 shift solenoid137 is on or energized in the D position-1st speed, D position- 2ndspeed and is off or de-energized in the D position- 3rd speed and Rposition. In the 2 and L positions of the manual valve 120, the 2-3shift solenoid 137 does not participate in the control operation sincethe fluid .passage 126 is exhausted in such positions regardless of theenergization or de-energization of the solenoid 137 and no fluid issupplied to the rear clutch servo chamber 7a or to the release side 22bof the servo for the front brake band 22. Further, in the R position ofthe manual valve 120, the 2-3 shift solenoid 137 does not participate inthe control operation since the fluid passage 124 is exhausted in suchposition, to exhaust the chamber 124' regardless of the energization anddeenergization of the solenoid 137 with the result that the 2-3 shiftvalve element 136 is urged to its rightward position and the fluidpassage 128 communicates with a fluid passage 139. The symbols and Xshow that a specific hydraulic servo is in operation and not inoperation respectively. In the L position-1st speed, the oneway clutch23 becomes engaged upon the operation of the engine to apply a drivingforce to the output shaft of the transmission. Further, as will beapparent from Table l, the vehicle is running at the L position-1stspeed, 2 position-2nd speed and D position3rd speed. When no current issupplied to both the l-2 and 2-3 shift solenoids 132 and 137, that is,when both these solenoids are in the off state. Thus, the vehicle canrun unhindered even when no current is supplied to these solenoids dueto trouble occurred in the electrical control section of the system.

A shift shock control solenoid 140 is provided to connect and disconnectthe fluid passage 134 leading from the l-2 shift means 130 to the applyside 22a of the servo for the front brake band 22 with the fluid passage139 leading from the 2-3 shift means 135 to the release side 22b of theservo for the front brake band 22 and to the rear clutch servo chamber7a. The solenoid has a structure similar to that of the l-2 shiftsolenoid 132. When current is supplied to the solenoid 141), the fluidpassage 134 is connected with the fluid passage 139 through an orifice142, and when no current is-supplied to the solenoid 140, the orifice142 is closed by a plunger 141 to interrupt the connection between thefluid passages 134 and 139.

In response to the movement of the shift valve elemerits in the mannerabove described, fluid is supplied to or discharged from the apply andrelease sides 22a and 22b of the servo for the front brake band 22 andto or from the rear clutch servo chamber 7a to engage or disengage thebrake band and clutch thereby to shift the gear position. In this case,a so-called shift shock occurs due to a variation in the torque andrevolutions of the members of the transmission and the engine. Thisshift shock can be alleviated by controlling the engaging or disengagingrate and the engaging or disengaging timing of the clutch and brakeband. In response to a signal applied from the electrical controlsection of -the system, the shift shock control solenoid 140 controlsthe rate of increase or decrease in the servo fluid pressure or fluidpressure in the fluid passages 139 and 134 during the shift so as tocontrol the engaging rate and timing of the clutch and brake band forensuring a smooth shift. The rate of increase or decrease in the servofluid pressure can be controlled by various methods including a methodin which the current supplied to the pressure regulating solenoid isvaried to cause oscillation of the solenoid thereby controlling theleakage. In the present invention, a simpler method is employed in whichan increase in the servo fluid pressure when a constant amount of fluidis allowed to leak through the orifice 142 is suitably combined with anincrease in the servo fluid pressure when no fluid is allowed to leakthrough the orifice 142 so as to obtain the optimum increase in theservo fluid pressure for ensuring a smooth shift. The shift shockcontrol solenoid 140 is capable of alleviating the shift shock occurringduring an upshift from the first to second speed (hereinafter to bereferred to as 1-2 upshift), an upshift from the second to third speed(hereinafter to be referred to as a 2-3 upshift), a downshift from thethird to second speed (hereinafter to be referred to as a 3-2downshift), and a shift from the neutral or N position to the reverse orR position (hereinafter to be referred to as an N-R shift).

The operation of the shift shock control solenoid 140 during theseshifts will now be described.

l-2 upshift In the first speed position, the front clutch 6 and onewayclutch 23 are actuated, while in the second speed position, the frontbrake band 22 is engaged. in order to carry out this shift smoothly, thefront brake band 22 -is preferably engaged-at a suitable rate. FIG. 4shows ply of current to the shift shock control solenoid 140, the fluidpassage 134 communicates with the fluid passage 139 through the orifice142. Since the 2-3 shift solenoid 137 is energized and the 2-3 shiftvalve element 136 is-biased to its rightward position in the secondspeed position, the fluid passage 139 communicates with the fluidpassage 128 and is exhausted through an orifice 128a and a check valvel28b in the fluid passage 128 and through the manual valve 120.Therefore, the fluid pressure in the fluid passage 134 leading to theapply side 22a of the servo for the front brake band 22 increases slowlyas shown by the curve b in FIG. 4. The rate of increase in the fluidpressure can be regulated by suitably selecting the size or diameter ofthe orifices 134a and 142. It is therefore possible to obtain a curvewhich is intermediate between these two curves a and b and gives apreferred rate of increase in the fluid pressure by suitably energizingand de-energizing the shift shock control solenoid 140 after the l-2shift valve element 132 has been urged to the leftward (extended)position in response to the shift signal. Generally, prematureengagement of the clutch and brake band re sults in a large shift shockand in a reduction of the service life of the linings of the clutch andbrake band due to anincrease in the amount of energy absorbed by theclutch and brake band linings per unit time. Also, when the clutch andbrake band are engaged too late, a similar reduction in the service lifeof the linings results from the speeding up of the engine, anuncomfortable feeling and an increase in the amount of energy absorbedby the linings per unit time. It is therefore necessary to engage theclutch and brake band at a suitably controlled rate which is neither tooearly nor too late. The curve 0 in FIG. 4 shows a moderate rate ofincrease in the fluid pressure. More precisely, the shift shock controlsolenoid 140 is kept in the de-energized state for a period of time t,starting from the point 0 at which the shift signal was applied to thel-2 shift means 130 until a point A, is reached. At this point. A,, theshift shock control solenoid 140 is energized and is kept in such statefor a period of time t until a point A is reached. At this point A theshift shock control solenoid 140 is de-energized again and is kept insuch state thereafter. A very smooth shift can be carried out when theperiods of time t and t in this curve c are controlled so that theengagement of the front brake band 22 is started in the vicinity of thepoint A and is ended to complete the shift in the vicinity of the pointA,. The number of on-off cycles of the shift shock control solenoid 140may be increased when a more complex curve is required to carry out asmooth-shift. Further, the l-2 upshift can be attained smoothly underall the driving conditions of the vehicle by varying the points A and Ahence the periods of time 2, and t depending on the driving conditionssuch as, for example, the engine torque, vehicle speed and temperatureof lubricating oil. The on-off control of the shift shock controlsolenoid 140 will be described in detail in the later descriptionrelating to the electrical control section of the control system. Wheresuitable change-over between the curves a and b, hence the on-off of theshift shock control solenoid 140 solely cannot give a satisfactory rateof increase in the fluid pressure in certain driving conditions, anorifice control valve actuated by the shift shock control solenoid 140may be put into the fluid passage 134 and associated with a plurality oforifices so as to selectively direct fluid flow through all or one ofthese orifices as will be described later.

2-3 upshift In an upshift from the second to third speed, the 1-2 shiftvalve element 131 is kept in its leftward (retracted) position and the2-3 shift valve element 136 is urged to its leftward (retracted)position to release the front brake band 22 and engage therear clutch 7.

In this case, the control of the disengaging timing of the front brakeband 22, the engaging timing of the rear clutch 7 and the rate ofengaging the rear clutch 7 is important in order to carry out the 23upshift smoothly. In the de-energized state of the shift shock controlsolenoid 140, fluid under pressure is supplied to the fluid passage 139through the orifice 126a. However, in response to the energization ofthe shift shock control solenoid 140, the fluid passage 139 communicateswith the fluid passage 134 so that fluid is also supplied to the fluidpassage 139 from the fluid passage 134, and at the same time, fluidflowing through the fluid passage 134 to be supplied to the apply side22a of the servo for the front brake band 22 leaks through the orifice142 and thus fluid pressure is reduced to a suitable level correspondingto the fluid pressure in the fluid passage 139. Therefore, the fluidpressure in the fluid passage 139 to be supplied to the release side 22bof the servo for the front brake band 22 is lower in the energized stateof the solenoid than when the solenoid 140 is in the de-energized state,and the front brake band 22 is disengaged by such a lower fluidpressure. In this manner, the timing of the engaging of the rear clutch7 and the timing of the disengaging of the front brake band 22 can bevaried. The timing can be varied by suitably energizing andde-energizing the shift shock control solenoid 140 after the applicationof a 2-3 upshift signal as in the case of the l-2 upshift. That is, asmooth 2-3 upshift can be attained by the on-off control of the shiftshock control solenoid '140 thereby varying the rate of decrease in thefluid pressure supplied to the apply side 22a of the servo for the frontbrake band 22, the rate of increase in the fluid pressure supplied tothe release side 22b of the servo for the front brake band 22, and therate of increase in the fluid pressure supplied to the rear clutch servochamber 7a. In an arrangement shown in FIG. 5, two shift shock controlsolenoids 140 and 140' are associated with the fluid passages 134 and139 respectively for controlling the rate of decrease in the fluidpressure supplied to the apply side 22a of the servo for thefront brakeband 22 and the rate of increase in the fluid pressure supplied to therear clutch servo chamber 7a independently of each other. By thisarrangement, the engage timing of the rear clutch 7, the disengagetiming of the front brake band 22 and the rate of engaging the rearclutch 7 can be more accurately controlled than the arrangement shown inFIG. 3.

3-2 downshift In a downshift from the third to second speed, the 2-3shift valve element 136 is urged to its rightward position from thethird speed position to exhaust the fluid passage 139 leading to therelease side 22b of the servo for the front brake band 22 and to therear clutch servo chamber 7a, and the piston in the front brake band 22is urged to the engaging position. In this case too, the fluid passage134 communicates with the fluid passage 139 in response to theenergization of the shift shock control solenoid 140 and fluid leaksthrough the orifice 142 so that the engage timing of the front brakeband 22 can be suitably delayed relative to the disengage timing of therear clutch 7 and the front brake band 22 can be engaged at a moderaterate. Thus, the front brake band 22 can be engaged at a suitable ratewith suitable timing and the rear clutch 7 can be disengaged withsuitable timing depending on the on-off control of the shift shockcontrol solenoid 140 thereby attaining a smooth 3-2 downshift.

N-R shift In reversing, the rear brake band 21 and the rear clutch 7 areactuated. The fluid passage 139 leading to the rear clutch servo chamber7a communicates with the fluid passage 134 in response to theenergization of the shift shock control solenoid 140. In the R positionof the manual valve 120, the fluid passage 134 is exhausted through theorifice 134a, check valve 134b and fluid passage 125. Therefore, in theenergized state of the shift shock control solenoid 140, fluid flowingthrough the fluid passage 139 leaks through the orifice 142 and fluidpressure supplied to the rear clutch servo chamber 7a by way of thefluid passage 139 increases at a moderate rate. That is, the rear clutchservo pressure can be increased at a suitable rate and the N-R shift canbe attained smoothly when the shift shock control solenoid 140 isenergized and de-energized after the N-R shift as in the case of the I2upshift.

In a modification shown in FIG. 6a, a fluid pressure regulating valve145 is placed in the fluid passage 134 leading to the hydraulic servofor the front brake band 22. In this arrangement, a variation in thefluid pressure in a valve chamber 144 due to the on-off of the shiftshock control solenoid 140 is utilized to control the rate of increasein the fluid pressure supplied to the servo. By this arrangement,delicate control of the rate of increase in the fluid pressure can beattained compared with the control solely with the orifice shown in FIG.5. In another modification shown in FIG. 612, an orifice control valve145 is placed in the fluid passage 134 leading to the hydraulic servofor the front brake band 22 and is responsive to the on-off operation ofthe shift shock control solenoid 140 to change over orifices 134a and134a to attain a required increase in the servo fluid pressure. Theorifice control valve 145' is in the illustrated position when the shiftshock control solenoid 140 is in the de-energized state, and in thisposition of the valve 145, fluid is supplied to the apply side 22a ofthe servo for the front brake band 22 through both the orifices 134a and134a. When the solenoid 140 is energized, the valve 145' is urged to itsrightward position with the result that fluid is supplied'through theorifice 134a only. Further, fluid leaks through an orifice 134a. Thus,fluid pressure supplied to the servo is reduced compared with thatsupplied in the deenergized state of the solenoid 140. A rate ofincrease in the fluid pressure as shown in FIG. 4 can also be obtainedby the utilization of these means.

The electrical control section of the system adapted for carrying outvarious kinds of control as above described by controlling the solenoidsI15, 132, 137 and 140 will be described with reference to FIG. 7.

Referring to FIG. 7, the electricalcontrol section includes a throttleposition detector 200, an engine r.p.m. detector 220, and an outputshaft r.p.m. detector 240 for detecting the parameters required forshift control and fluid pressure control; a l-2 shift discriminatingcircuit (D) 300, a ]2 shift discriminating circuit (L) 300, a 2-3 shiftdiscriminating circuit 320, and a discriminating circuit 340 forcarrying out necessary computations on the signals supplied from thedetectors and feedback circuits 310, 310 and 330 associated with therespective discriminating circuits 300, 300' and 320; a timingcontroller including an N(P)-R shift timing control circuit 420a, a 3-2downshift timing control circuit 420b, a 2-3 upshift timing controlcircuit 420s and a [-2 upshift timing control circuit 420d forcontrolling the shift shock solenoid amplifiers 450, 460, 470 and 480for amplifying the signals to a level sufficient to energize therespective solenoids 132, 115, 137 and 140; a shift position switch 260;a reference voltage supply 350; and a power regulator 700 for regulatingthe voltage supplied from the positive terminal of a battery. Thepositive terminal of the battery is connected through an ignition switchand a fuse to the power regulator 700 which distributes the power to thecircuits above described by regulating the battery voltage to a voltagelevel suitable for the control of these circuits.

The shift position switch 260 comprises a movable contact strip 261arranged for interlocking operation with the shift lever disposedadjacent to the drivers seat and a plurality of stationary contacts, andthe battery voltage appears at output leads 265, 266, 267 and 268depending on the R, D, 2 and L positions respectively of the manualvalve 120.

The throttle position detector 200 has a structure as shown in FIG. 8.The throttle position detector 200 includes a throttle positiondetecting means 202 in the form of a muIti-contact switch which isresponsive to the position of the throttle valve in the carburetor orresponsive to the actuation of the accelerator pedal. This switch mayrespond to a mechanical displacement representative of the negativepressure in the air intake manifold inasmuch as it is an engine torqueresponsive signal detecting means. The multi-contact switch 202 isprovided with a movable contact 203 and a plurality of stationarycontacts 204, 205, 206 and 207 and is so constructed that the movablecontact 203 is successively brought into contact with the stationarycontacts 204, 205, 206 and 207 as the opening S, of the throttle valveis successively increased to S S S and S The stationary contacts 204,205, 206 and 207 and the movable contact 203 are connected with one endof the respective variable resistors 210, 211, 212, 213 and 214. Thestationary contact 205 is further connected with an output terminal 201and the movable contact 203 is connected with the power supply ofvoltage E The variable resistors 210, 211, 212, 213 and 214 are groundedat the other end through a resistor 215, and the junction point betweenthese variable resistors and the resistor 215 is connected with anoutput terminal 201. The variable resistor 214 is so adjusted that avoltage E appears at the output terminal 201 when S, S due to the fullclosure of the throttle valve in the carburetor. Then, when the throttlevalve opening 8, is increased to S the movable contact 203 engagessolely with the stationary contact 204. The variable resistor 210 is soadjusted that the output appearing at the output terminal 201 in such aposition of the switch 202 is given by [R/(R, R, R)]E E where R, R, andR, are the resistances of the resistor 215, variable resistor 210 andvariable resistor 214 respectively and R R is the resistance given whenthe variable resistors 210 and 214 are connected in the circuit inparallel with each other. Similarly, the variable resistors 211, 212 and213 are so adjusted that the outputs appearing at the output terminal201 in response to the throttle valve openings of S S and S are given byE E and E respectively. Thus, the voltages E E E E and E appear at theoutput terminal 201 in response to the throttle valve opening S of S S SS and S respectively. In other words, a stepped signal voltage E (N 0,l, 2, 3, 4)" appears at the output terminal 201 depending on thethrottle valve opening. This signal voltage is called hereinafter athrottle position signal E0. The switch 202 is shown as having fourstationary contacts, but it is apparent that the number of stationarycontacts may be increased when it is desired to obtain a more complexstepped signal. The voltage E appears at the output terminal'201 whenthe throttle valve opening 8, is S em and over. This voltage is calledhereinafter a preset throttle opening signal.

The output shaft r.p.m. detector 240 is connected to a D-A converter250. The structure and operation of the output shaft r.p.m. detector 240will be described with reference to FIGS. 9a and 9b. The output shaftr.p.m. detector 240 comprises an r.p.m. detecting means 242 mounted onthe transmission housing 30 and a toothed disc 243 secured to the outputshaft 18 of the transmission. Suppose that the number of teeth of thetoothed disc 243 is N, then the r.p.m. detecting means 242 detects ana.c. voltage signal S having a frequency which is N times the number ofrevolutions n of the output shaft 18. Thus, S n X N. Knowing the numberof revolutions n of the output shaft 18 enables the speed of the vehicleto be known. As seen in a side elevation in FIG. 9a, the toothed disc243 which is secured at its center of rotation to the output shaft 18 isa disc-plate of magnetic material having N equally spaced teeth formedalong its circumference, and the r.p.m. detecting means 242 is mountedon the transmission housing 30 at a position closely adjacent to thetoothed disc 243 in the diametral direction of the latter. The r.p.m.detecting means 242 is composed of a permanent magnet 91 and a coil 92wound around the magnet 91. The permanent magnet 91 and the coil 92 arehoused in a suitable casing of non-magnetic material and the casing ismounted on the transmission housing 30 so that one end of the permanentmagnet 91 is disposed in close'proximity to the outer periphery of thetoothed disc 243. As the tooth portion of the toothed disc 243 passesthrough the magnetic field of the permanent magnet 91 due to therotation of the toothed disc 243, a variation takes place in the leakageflux of the permanent magnet 91 so that an electromotive force isproduced in the coil 92. One complete rotation of the toothed disc 243produces N voltage pulses, and as described previously, a voltage signalat an a.c. voltage S having a frequency n X N is obtained when theoutput shaft 18 rotates at a number of revolutions n per unit time. Thisvoltage signal appears across output terminals 93. It will be apparentfor those skilled in the art that the detection of the speed of thevehicle can be attained by various other methods including 6 mounting asmall-sized generator in coaxial relation with the driven gear connectedto the speed meter and detectinG the output from the generator.

The output voltage signal S delivered from the output shaft r.p.m.detector 240 is applied through a lead 251 to the DA converter 250. TheD-A converter 250 converts the a.c. signal or digital signal S into adc. signal or analog signal. The D-A converter 250 has a structure asshown in FIG. 10. The input voltage signal S is applied by the lead 251to an amplifier 253 in which the amplitude of the signal is increased.An amplitude limiter 254 limits the amplitude of the signal to a fixedvalue. A frequency detecting, rectifying and amplifying circuit 255converts the a.c. voltage into a dc. voltage which is then led out by alead 252. This voltage is proportional to the r.p.m. of the output shaft18 and will hereinafter be called an output shaft r.p.m. signal orvehicle speed signal E The l-2 shift discriminating circuit (D) 300 andthe associated feedback circuit 310 have a structure as 7 shown in FIG.11. The discriminating circuit 300 includes a comparator 305 of anysuitable type presently commercially available such as those sold underthe trade names Ofp. Fe 71 by Nippon Electric Co., Ltd. or of SN727l0Nby Texas Instruments Co., Ltd. An ihput resistor 306 is connected at oneend to one of the input terminals 305a of the comparator 305 and at theother end to the movable arm of a variable resistor 307. The variableresistor 307 is connected across the input terminals 303 and 304 of thediscriminating circuit 300. An input resistor 308 is connected at oneend to the other input terminal 305!) of the comparator 305 and at theother end to the movable arm of a variable resistor 309. The variableresistor 309 is connected at one end to the input terminal 302 of thediscriminating circuit 300 and is grounded at the other end. Terminals3050, 305d and 305a connect the comparator 305 to the positive terminalof the power supply, to the negative terminal of the power supply and toground respectively. The feedback circuit 310 is composed of atransistor 311, a resistor 312 and a variable resistor 313. Thetransistor 31 1 has its emitter grounded and its base connected to theoutput lead 301 of the discriminating circuit 300 through the resistor312. The collector of the transistor 311 is connected to one end of thevariable resistor 313, and this junction point is connected to the inputterminal 304 of the discriminating circuit 300. The movable arm of thevariable resistor 313 is grounded.

In operation, assuming that a voltage or 1 appears on the output lead301 when no signal is applied to the input terminals 302 and 303 of thediscriminating circuit 300, the transistor 311 in the feedback circuit310 is conducting due to the supply of base current through the resistor312 and the input terminal 304 is substantially grounded. Then, when anoutput shaft r.p.m. signal E, and a throttle position signal E, areapplied to the respective input terminals 303 and 302 of thediscriminating circuit 300, a voltage E, [R /(R R,,)] E, appears at themovable arm of the variable resistor 307, where R, is the resistancebetween the input terminal 303 and the movable arm of the variableresistor 307, and R,, is the resistance between the movable arm of thevariable resistor 307 and the collector of the transistor 31] in thefeedback circuit 310. A voltage E 9 4=[R /(R +R -E appears at themovable arm of the variableresistor 309, where R is the resistanceBasses theinput tei minal 302 and the variable arm of the variableresistor 309, and R is the resistance between the movable arm of thevariable resistor 309 and ground. Thus, the voltage E, is applied to theinput terminal 305a of the comparator 305 through the input resistor306, and the voltage E, is applied to the input terminal305b of thecomparator 305 through the input resistor 308. The comparator 305compargs the voltage E with the voltage En. When E,.'* is positive,,nooutput signal or 0 is delivered from the comparator 305, while when E Eis negative, an output signal or 1 is delivered from the comparator 305to appear on the output lead 301. The resistors 306 and 308 areprotective resistors which protect the comparator 305 against largeinputs that may be applied to the input terminals.

When no output signal or appears on the output lead 301 of thediscriminating circuit 300, due to E E9 0, no base current is suppliedto the transistor 311 through the resistor 312 in the feedback circuit310, it is possibletoseek the""EeIatioii E AFg age 12,, [(R,, R )/(R RR,)] -E,, is applied to the input terminal 305a of the comparator 305,where R is the resistance of the variable resistor 313. Thus, E,," E,for the same value of E,,. It will be understood therefore that theoutput appearing on the output lead 301 of the comparator 305 changesfrom 0 to 1 at a lower value of E or at a lower vehicle speed than whenthe output changes from 1 to 0. In other words, the feedback circuit 310acts to vary the degree of modification of the output shaft r.p.m.signal E, by the resistors depending on the appearance of 0 or 1 on theoutput lead 301 of the discriminating circuit 300 thereby varying theconditions of discrimination by the discriminating circuit 300. Thismethod is effective to stabilize the signal appearing on the output lead301 and to prevent undesirable hunting between 0 and 1.

By suitably selecting the resistances of the variable resistors 307, 309and 313 in the l-2 shift discriminating circuit (D) 300 and theassociated feedback circuit 310, it is possible to seek the relation E"AE between the output shaft r.p.m. signal E and the throttle positionsignal E when the output appearing on the output lead 301 changes from 1to 0, and the relation E,, A'E between these two signals when the outputappearing on the output lead 301 changes from O to 1. These relationsare shown in FIG. 12. It will be seen from FIG. 12 that the outputappearing on the output lead 301 changes from 1 to 0 or no outputvoltage appears on the output lead 301 when E,, is increased to make ashift into the region on the right-hand side of the line representingthe relation E,,=A E The output appears on the output lead 301 againwhen E is decreased while 0 is appearing on the output lead 301 to suchan extent that the relation E A 'E holds.

The output signal delivered from the discriminating circuit 300receiving the throttle position signal E AND circuit 500 which receivesanother input signal from an OR circuit 501. A switching circuit (D) 273applies its output signal to one of the two input terminals of the ORcircuit 501, while a switching circuit (2) 2 74 applies its outputsignal to the other input terminal of the OR circuit 501. Theseswitching circuits 273 and 274 are switching relays employingtransistors therein and deliver an output signal of I when the shiftlever actuating the manual valve 120, hence the shift position switch260 takes its D and 2 positions respectively. These switching circuits273 and 274 deliver no output signal or 0 in the other positions of theshift position switch 260. Thus, the OR circuit 501 delivers an outputsignal or 1 in the D and 2 positions while it delivers no output signalor 0 in the other positions of the shift position switch 260. Therefore,the AND circuit 500 delivers an output signal or 1 in response to theapplication of 1 from the l2 shift disciminating circuit 300 in the Dand 2 positions only of the shift position switch 260, and this outputsignal is applied through an OR circuit 502 to the amplifier 450, thenceto the l2 shift solenoid 132 for energizing same. The AND circuit 500and the OR circuits 501 and 502 are of the construction well-known inthe art, and the amplifier 450 amplifies the output signal from the ORcircuit 502 to a level enough to energize the 12 shift solenoid 132.

The l2 shift discriminating circuit (L) 300 and the associated feedbackcircuit 310' have a structure and function similar to those of the l2shift discriminating circuit (D) 300 and the associated feedback circuitHowever, the input terminals of the discriminating circuit 300 receivingthe throttle position signal E and the output shaft r.p.m. signal E, arereversed from the case of the discriminating circuit 300 so as to seekthe relation E,, CE 9 between these two signals when the outputappearing on an output lead 301' changes from 0 to 1 and the relation EC'E between these two signals when the output appearing on the outputlead 301 changes from 1 to 0. These relations are also shown in FIG. 12.Thus, the 1-2 shift discriminating circuit (L) 300' delivers an outputsignal or 1 when E, CE whereas the 12 shift discriminating circuit (D)300 delivers no output signal or 0 when E,.- AEg. The output signaldelivered from the 12 shift discriminating circuit 300 is applied as oneof inputs to an AND circuit 503 of known construction which receivesanother input signal from a switching circuit (1.) 275. The switchingcircuit (L) 275 delivers an output signal or 1 in the L position of thetransmission shift lever and no output signal or 0 in any otherpositions of the shift lever. Therefore, the l2 shift discriminatingcircuit (L) 300 delivers an output signal 05 1 when E" 2 CE; and theswitching circuit (L) an output signal or 1 in the L position of theshift lever only. In response to the application of these two signals,the AND circuit 503 delivers an output signal or 1. This signal isapplied to the amplifier 450 through the OR circuit 502 for energizingthe 12 shift solenoid 132. It will be seen that two discriminatingcircuits are provided to produce the signal for energizing the l2 shiftsolenoid 132 in the different positions of the transmission shift lever.These two disciminating circuits are required so that the [-2 shiftsolenoid 132 is on in the D position-1st speed, 2 position-1st speed andL position- 2nd speed and off in the position-2nd speed, 2 position- 2ndspeed and L position-1st speed as shown in Table 1. However, it isapparent that any other suitable means may be employed to reverse the onand off state of the l2 shift solenoid 132 in the first and secondspeeds in the manner above described. According to the presentinvention, the range of the first speed in the D and 2 positions can bevaried greatlyfrom the range of the first speed in the L position asseen in FIG. 12 by virtue of the provision of the two discriminatingcircuits.

The function of the 2-3 shift discriminating circuit 320 and theassociated feedback circuit 330 is similar to that of the l2 shiftdiscriminatingcircuit (D) 300 and the associated feedback circuit 310described previously. The 2-3 shift discriminating circuit 320 com-

1. In an automatic automotive vehicle transmission used for transmittingtorque between a driving shaft and a driven shaft, a control systemcomprising: frictional engaging means provided with fluid pressureoperated servo means for selective actuation thereof and arranged forthe transmission of torque between said driving and driven shafts, asource of fluid pressure for supplying fluid under pressure foractuating said frictional engaging means by selective application tosaid servo means, fluid passage means leading from said fluid pressuresource to said frictional engaging means, fluid passage change-overvalve means disposed in said fluid passage means for selectivelydistributing fluid under pressure to predetermined servo means in saidfrictional engaging means, signal generator means including a signalgenerator for generating a first electrical signal responsive to atleast one of the running conditions of the vehicle, fluid pressurecontrol means for controlling the pressure of fluid supplied to saidfrictional engaging means through said fluid passage change-over valvemeans, and timing control means for generating a second electricalsignal and means for controlling the operation timing of said fluidpressure control means in response to the first electrical signaldelivered from said signal generator means, whereby said fluid pressurecontrol means is subject to on-off control during a shift from one gearposition to another which is followed by a variation in the torque beingtransmitted between said driving and driven shafts so as to control thefluid pressure supplied to said frictional engaging means therebyensuring smooth transmission of the torque between said driving anddriven shafts during the shift.
 2. In an automatic automotive vehicletransmission used for transmitting torque between a driving shaft and adriven shaft, a control system comprising: frictional engaging meansprovided with fluid pressure operated servo means for selectiveactuation thereof and arranged for the transmission of torque betweensaid driving and driven shafts, a source of fluid pressure for supplyingfluid under pressure for actuating said frictional engaging means byselective application to said servo means, fluid passage means leadingfrom said fluid pressure source to said frictional engaging means, shiftvalve means disposed in said fluid passage means for selectivelydistributing fluid under pressure to predetermined servo means in saidfrictional engaging means, means for generating an electrical signalresponsive to the engine torque, means for generating an electricalsignal responsive to the vehicle speed, shift signal computing means forcomputing the relation between these two electRical signals and forgenerating a shift signal when the relation between these two signalssatisfies a predetermined condition, fluid pressure supply control valvemeans for allowing leakage of fluid under pressure in said fluid passagemeans leading to said frictional engaging means through said shift valvemeans thereby controlling the fluid pressure supplied to said frictionalengaging means, and timing control means for generating a timing controlsignal in response to the output signal delivered from said shift signalcomputing means for controlling the period of time of the leakage offluid under pressure from said fluid passage means through said fluidpressure supply control valve means, whereby said fluid pressure supplycontrol valve means controls the rate of increase or decrease relativeto time of the pressure of fluid supplied to said frictional engagingmeans for ensuring smooth transmission of the torque between saiddriving and driven shafts during a shift from one gear position toanother.
 3. In an automatic automotive vehicle transmission used fortransmitting torque between a driving shaft and a driven shaft, acontrol system comprising: a first frictional engaging means providedwith a fluid pressure operated servo means for establishing a high speeddrive ratio between said drivingand driven shafts, a second frictionalengaging means provided with a fluid pressure operated servo meanshaving an apply-side chamber and a release-side chamber for establishinga low speed drive ratio between said driving and driven shafts, a sourceof fluid pressure for supplying fluid under pressure for actuating saidfrictional engaging means, a plurality of shift valves for selectivelydistributing fluid under pressure to said frictional engaging means, afirst fluid passage leading from one of said shift valves to theapply-side chamber of said fluid pressure operated servo means for saidsecond frictional engaging means, a second fluid passage leading fromanother said shift valve to the fluid pressure operated servo means forsaid first frictional engaging means and to the release-side chamber ofsaid fluid pressure operated servo means for said second frictionalengaging means, a fluid pressure supply control valve connected to saidfirst and second fluid passages for connecting and disconnecting theapply-side servo chamber with the release-side servo chamber with therelease-side servo chamber of said fluid pressure operated servo meansfor said second frictional engaging means thereby controlling the fluidpressure supplied to said second frictional engaging means, signalgenerator means including a signal generator for generating anelectrical signal responsive to at least one of the running conditionsof the vehicle, and timing control means for generating a timing controlsignal for controlling the operation timing of said fluid pressuresupply control valve in response to the output signal delivered fromsaid signal generator means, whereby said fluid pressure supply controlvalve controls the fluid pressure supplied to both of said frictionallyengaging means during a shift from one gear position to another which isfollowed by a variation in the drive ratio between said driving anddriven shafts so as to ensure a smooth transition from one gear positionto another.
 4. In an automatic automotive vehicle transmission used fortransmitting torque between a driving shaft and a driven shaft, acontrol system comprising: a first frictional engaging means providedwith a fluid pressure operated servo means for establishing a high speeddrive ratio between said driving and driven shafts, a second frictionalengaging means provided with a fluid pressure operated servo meanshaving an apply-side chamber and a release-side chamber for establishinga low speed drive ratio between said driving and driven shafts, a sourceof fluid pressure for supplying fluid under pressure for actuating saidfriCtional engaging means, a plurality of shift valves for selectivelydistributing fluid under pressure to said frictional engaging means, afirst fluid passage leading from one of said shift valves to theapply-side chamber of said fluid pressure operated servo means for saidsecond frictional engaging means, a second fluid passage leading fromanother said shift valve to the fluid pressure operated servo means forsaid first frictional engaging means and to the release-side chamber ofsaid fluid pressure operated servo means for said second frictionalengaging means, an electromagnetically operated fluid pressure controlvalve connected with at least one of said first and second fluidpassages for allowing leakage of fluid under pressure in said fluidpassage, signal generator means including a signal generator forgenerating an electrical signal responsive to at least one of therunning conditions of the vehicle, and timing control means forgenerating a timing control signal for controlling the operation timingof said electromagnetically operated fluid pressure control valve inresponse to the output signal delivered from said signal generatormeans, whereby said electromagnetically operated fluid pressure controlvalve controls the fluid pressure supplied to said frictional engagingmeans during a shift from one gear position to another which is followedby a variation in the drive ratio between said driving and driven shaftsso as to ensure a smooth transition from one gear position to another.5. A control system for an automatic transmission as in claim 1, inwhich said fluid pressure control means comprises: anelectromagnetically operated valve allowing leakage of fluid underpressure in said fluid passage means, and a valve for regulating thepressure of fluid, said electromagnetically operated valve and saidfluid pressure regulating valve cooperating to control the fluidpressure supplied to said frictional engaging means.
 6. A control systemfor an automatic transmission as in claim 1, in which said fluidpressure control means comprises: an electromagnetically operated valvefor draining fluid in said fluid passage means, and an orifice controlvalve, said electromagnetically operated valve and said orifice controlvalve cooperating to control the fluid pressure supplied to saidfrictional engaging means.
 7. In a control system for an automatictransmission comprising a plurality of frictional engaging means, eachhaving fluid control means associated therewith for selectivelyeffecting shift changes in torque transmitted between a driving and adriven shaft, an improvement comprising: fluid pressure modifying meansfor modulating normal selective changes in the fluid pressure applied tosaid fluid control means to effect desired shift changes in transmittedtorque, and control means connected to said fluid pressure modifyingmeans for controlling the timing and degree of modulation to effect asmooth change in the transmitted torque through said transmission duringsaid desired shift changes.
 8. improvement as in claim 7 wherein: saidfluid pressure modifying means comprises at least one controllablyopened or closed valve in fluid communication between a fluid passagehaving low fluid pressure during a given shift change and at least onefluid passage leading to a fluid control means having high pressureapplied thereto for effecting said given shift, the rate of increase ofpressure in said at least one fluid passage being effectivelycontrollable by opening and closing said valve in response to an appliedtiming control signal, and said control means comprises means fordetecting an impending shift change and for generating said timingcontrol signal having a predetermined timing and duration with respectto the shift change being effected.
 9. An improvement as in claim 8wherein said valve comprises an orifice and means for closing andopening said orifice eleCtromagnetically.
 10. An improvement as in claim8 wherein said valve comprises a pressure regulating valve andassociated means for effecting electromagnetic control thereof.
 11. Animprovement as in claim 8 wherein said valve is connected between fluidpassages leading to two different ones of said fluid control means.